NOVEL MEDICAL USE FOR GABA AGONISTS

Abstract: The present invention relates to the use of GABA agonists having an agonist action at GABAB receptors in the treatment of emesis.

Description: Novel Medical Use for GABA Agonists The present invention relates to the use of γ-aminobutyric acid (GABA) agonists having an agonist action at GABA B receptors in the treatment of emesis. GABA is an endogenous inhibitory neurotransmitter in the CNS and peripheral nervous systems. Receptors for GABA have been divided into GABA/ and GABAβ receptor sub-types. GABAg agonists are described as being of use in the treatment of CNS disorders, such as muscle relaxation in spinal spasticity, cardiovascular disorders, asthma, gut motility disorders such as irritable bowel syndrome and as prokinetic and anti-tussive agents. It has now been found that GABA agonists having an agonist action at GABA B receptors are useful in the treatment of emesis. The invention accordingly provides, in a first aspect, the novel use of GABA agonists having an agonist action at GABA B receptors in the treatment of emesis. There is also provided as a further aspect of the invention the use of GABA agonists having an agonist action at GABA B receptors in the preparation of a medicament for use in the treatment of emesis. In an alternative or further aspect there is provided a method for the treatment of a mammal, including man, suffering from or susceptible to emesis, comprising administration of an effective amount of a GABA agonist having an agonist action at GABA B receptors. There is an isolated report (The Lancet. July 23, 1983, pg. 227) that baclofen reduced the frequency of vomiting due to duodenal ileus in a patient with Duchenne muscular dystrophy. It is submitted that the use of (±) baclofen in the treatment of emesis caused by duodenal ileus is not included within the scope of the instant invention. Thus, according to a further aspect the invention provides the use of GABA agonists having an agonist action of GABA B receptors in the treatment of emesis with the proviso that, when the emesis is caused by duodenal ileus, the GABA agonist is other than (±) baclofen. It will be appreciated that reference to treatment is intended to include prophylaxis as well as the alleviation of established symptoms. GABA agonists having an agonist action at GABA B receptors have been shown to have anti-emetic activity as indicated by for example their ability to inhibit emesis induced by a variety of emetogens in the ferret. The treatment of emesis mentioned hereinbefore includes the treatment of nausea, retching and vomiting. Emesis includes acute emesis, delayed emesis and anticipatory emesis. GABA agonists having an agonist action at GABA B receptors are useful in the treatment of emesis however induced. For example, emesis may be induced by drugs such as cancer chemotherapeutic agents such as alkylating agents, e.g. cyclophosphamide, carmustine, lomustine and chlorambucil; cytotoxic antibiotics, e.g. dactinomycin, doxorubicin, mitomycin-C and bleomycin; anti-metabolites, e.g. cytarabine, methotrexate and 5- fluorouracil; vinca alkaloids, e.g. etoposide, vinblastine and vincristine; and others such as cisplatin, dacarbazine, procarbazine and hydroxyurea; and combinations thereof; radiation sickness; radiation therapy, e.g. irradiation of the thorax or abdomen, such as in the treatment of cancer; poisons; toxins such as toxins caused by metabolic disorders or by infection, e.g. gastritis; pregnancy; vestibular disorders, such as motion sickness or vertigo; post¬ operative sickness; gastrointestinal obstruction; reduced gastrointestinal motility; visceral pain, e.g. myocardial infarction or peritonitis; migraine; increased intercranial pressure; decreased intercranial pressure (e.g. altitude sickness); and opioid analgesics, such as morphine. Specific GABA agonists having an agonist action at GABA B receptors for use in the present invention include 4-amino-3-(5-chloro-2-thienyl)butyhc acid and those compounds generically and specifically disclosed in GB 1017439, e.g. baclofen, US 4656298, e.g. 3-aminopropylphosphonous acid (3- aminopropylphosphinic acid), EP 0356128, i.e. 3-(aminopropyl)methyl phosphinic acid, and EP0463969, e.g. 3-(2-imidazolyl)-4-aminobutanoic acid which disclosures are incorporated herein by reference. A particularly preferred compound for use in the present invention is baclofen. Baclofen, when used in the present invention, may be in the form of a mixture of isomers, for example a racemic mixture, or a separated isomer, i.e. the S(+) isomer or R(-) isomer. Preferably the R(-) isomer of baclofen is used. GABA B agonists may be administered as the raw chemical but are preferably presented as a pharmaceutical formulation. Suitable pharmaceutical formulations for GABA B agonists are described in the art. For example GABA B agonists may be formulated for oral, buccal, parenteral, depot or rectal administration or in a form suitable for administration by inhalation or insufflation (either through the mouth or nose). Oral and parenteral formulations are preferred. For oral administration, the pharmaceutical compositions may take the form of, for example, tablets or capsules prepared by conventional means with pharmaceutically acceptable excipients such as binding agents (e.g. pregelatinised maize starch, polyvinylpyrrolidone or hydroxypropyl methylcellulose); fillers (e.g. lactose, microcrystalline cellulose or calcium hydrogen phosphate); lubricants (e.g. magnesium stearate, talc or silica); disintegrants (e.g. potato starch or sodium starch glycollate); or wetting agents (e.g. sodium lauryl sulphate). The tablets may be coated by methods well known in the art. Liquid preparations for oral administration may take the form of, for example, solutions, syrups or suspensions, or they may be presented as a dry product for constitution with water or other suitable vehicle before use. Such liquid preparations may be prepared by conventional means with pharmaceutically acceptable additives such as suspending agents (e.g. sorbitol syrup, cellulose derivatives or hydrogenated edible fats); emulsifying agents (e.g. lecithin or acacia); non-aqueous vehicles (e.g. almond oil, oily esters, ethyl alcohol or fractionated vegetable oils); and preservatives (e.g. methyl or propyl- e-hydroxybenzoates or sorbic acid). The preparations may also contain buffer salts, flavouring, colouring and sweetening agents as appropriate. Preparations for oral administration may be suitably formulated to give controlled release of the active compound. For buccal administration the composition may take the form of tablets or lozenges formulated in conventional manner. The GABA B agonists may be formulated for parenteral administration by bolus injection or continuous infusion. Formulations for injection may be presented in unit dosage form e.g. in ampoules or in multi-dose containers, with an added preservative. The compositions may take such forms as suspensions, solutions or emulsions in oily or aqueous vehicles, and may contain formulatory agents such as suspending, stabilising and/or dispersing agents. Alternatively, the active ingredient may be in powder form for constitution with a suitable vehicle, e.g. sterile pyrogen-free water, before use. The GABA B agonists may also be formulated in rectal compositions such as suppositories or retention enemas, e.g. containing conventional suppository bases such as cocoa butter or other glycerides. The GABA B agonists may also be formulated as depot preparations. Such long acting formulations may be administered by implantation (for example subcutaneously or intramuscularly) or by intramuscular injection. Thus, for example, the compounds of the invention may be formulated with suitable polymeric or hydrophobic materials (for example as an emulsion in an acceptable oil) or ion exchange resins, or as sparingly soluble derivatives, for example, as a sparingly soluble salt. For intranasal administration, the GABA B agonists may be formulated as solutions for administration via a suitable metered or unit dose device or alternatively as a powder mix with a suitable carrier for administration using a suitable delivery device. Suitable dose ranges are described in the art, that is to say that for use as anti- emetics the compounds may be used at doses appropriate for other conditions for which GABA B agonists are known to be useful. It will be appreciated that it may be necessary to make routine variations to the dosage, depending on the age and condition of the patient, and the precise dosage will be ultimately at the discretion of the attendant physician or veterinarian. The dosage will also depend on the route of administration and the particular compound selected. A suitable dose range is for example 0.1 mg/kg to about 200mg/kg bodyweight per day. The GABA B agonists having an agonist action at GABA B receptors may, if desired, be administered in combination with one or more other therapeutic agents and formulated for administration by any convenient route in a conventional manner. Appropriate doses will be readily appreciated by those skilled in the art. For example, GABA agonists having an agonist action at GABA B receptors may be administered in combination with a systemic anti- inflammatory corticosteroid such as methyl prednisolone or dexamethasone, a 5HT3 antagonist such as ondansetron, granisetron or metoclopramide, or a tachykinin antagonist, including substance P antagonists and other neurokinin antagonists, such as an NK-| receptor antagonist. Biological Data The anti-emetic activity of (±) baclofen was demonstrated by its ability to inhibit emesis induced by radiation, cisplatin, morphine and ipecacuanha in the ferret. The anti-emetic activity of R(-) baclofen was demonstrated by its ability to inhibit radiation-induced emesis in the ferret. Radiation Test In this model of emesis the onset of retching and vomiting occurs approximately 20 minutes after whole body irradiation (2 Grey = 200 Rads). The test compound is administered (e.g. i.p., p.o., i.v., s.c.) immediately after irradiation and its effect on emesis determined by comparison with appropriate controls. (±) Baclofen inhibited emesis in the above test at 3mg/kg p.o. and 1mg/kg s.c. R(-) Baclofen inhibited emesis in the above test at 0.5 mg/kg s.c. S(+) Baclofen failed to inhibit emesis at 0.5 mg/kg s.c. Cisplatin Test In this model of emesis the onset of retching and vomiting occurs approximately 1 hour after the administration of cisplatin (200mg/m 2 i.p.). The test compound was administered (s.c.) 1 hour after the administration of the emetogen and its effect on emesis determined by comparison with appropriate controls (e.g. water). (±) Baclofen inhibited emesis in the above test at 1.0 mg/kg s.c. (±) Baclofen inhibited ipecacuanha - and morphine-induced emesis in ferrets at 1.0 mg/kg s.c.

Claims: Claims 1. The use of GABA agonists having an agonist action at GABA B receptors in the preparation of a medicament for use in the treatment of emesis. 2. A method for the treatment of a mammal, including man, suffering from or susceptible to emesis, comprising administration of an effective amount of a GABA agonist having an agonist action at GABA B receptors. 3. The use or method according to Claim 1 or Claim 2 wherein the GABA agonist is baclofen. 4. The use or method according to Claim 3 wherein baclofen is in the R (-) form. 5. The use or method according to any of Claims 1 to 4 wherein said emesis is induced by cancer chemotherapeutic agents, radiation sickness, radiation therapy, poisons, toxins, pregnancy, vestibular disorders, post-operative sickness, gastrointestinal obstruction, reduced gastrointestinal motility, visceral pain, migraine, increased intercranial pressure, decreased intercranial pressure, or opioid analgesics. 6. The use or method according to Claim 5 wherein said emesis is induced by a cancer chemotherapeutic agent, radiation sickness or radiation therapy. 7. The use or method according to Claim 6 wherein said cancer chemotherapeutic agent is selected from cyclophosphamide, carmustine, lomustine, chloroambucil, dactinomycin, doxorubicin, mitomycin-C, bleomycin, cytarabine, methotrexate, 5-fluorouracil, etoposide, vinblastine, vincristine, cisplatin, decarbazine, procarbazine, hydroxyurea, and combinations thereof. 8. The use or method according to Claim 7 wherein said emesis is induced by cisplatin. 9. The use or method according to Claim 7 wherein said emesis is induced by cyclophosphamide. 10. The use or method according to any of Claims 1 to 4 wherein said emesis is induced by morphine or ipecacuanha.

Inventors: BAYS DAVID EDMUND, BOUNTRA CHARANJIT, BAYS, DAVID, EDMUND, BOUNTRA, CHARANJIT
Applicants: BAYS DAVID EDMUND, BOUNTRA CHARANJIT, GLAXO GROUP LTD, BAYS, DAVID, EDMUND, BOUNTRA, CHARANJIT, GLAXO GROUP LIMITED
Application year: 1994
Main classification: A61K31
IPC codes: A61K31, A61K33, A61K45, A61P11, A61P25, A61P35, A61P43